1. Field of the Invention
The present invention relates to an ink jet recording apparatus capable of producing a high-quality image on a recording medium on which the image is to be recorded, and more particularly to an ink jet recording apparatus in which recording ink and an image quality improving agent for making insoluble or coagulating colorants mixed in the recording ink are ejected onto a recording medium.
2. Description of the Related Art
The present invention is applicable to all types of equipment for recording an image on recording media such as made of paper, cloth, leather, OHP and metal, for example, by utilizing thermal energy. Practical equipment adapted for application of the present invention include business machines, e.g., printers, copying machines and facsimiles, as well as industrial production machines.
An ink jet recording method has been hitherto used in printers and copying machines, for example, because of such advantages as low noise, low running cost, easiness in reducing the apparatus size, and easiness in printing an image in colors.
In an ink jet recording apparatus, ink is ejected from a nozzle to deposit on a sheet of recording paper, thereby forming an image. To improve a recording speed, a recording element and an ink ejection port and passage (nozzle) necessary for ejecting the ink are integrated and arrayed in plural number on a recording head (referred to as a multi-head hereinafter). An apparatus adapted for color recording includes a plurality of multi-heads.
FIG. 15 is a schematic perspective view of such an ink jet recording apparatus. A recording medium 106 inserted in a paper feed position of a recording apparatus 100 is advanced by a feed roller 109 to a recording enable area covered by a recording head unit 103. A platen 108 is provided to support a lower surface of the recording medium in the recording enable area. A carriage 101 is constructed to be movable in a direction determined by two guide shafts, i.e., a guide shaft 104 and a guide shaft 105, to reciprocally scan the recording enable area. On the carriage 101, there is mounted a recording head unit 103 comprised of recording heads for ejecting inks in plural colors and ink tanks for supplying the inks in plural colors to the recording heads, respectively. The illustrated ink jet recording apparatus employs inks in four colors, i.e., black (Bk), cyan (C), magenta (M) and yellow (Y). A restoration system unit 110 is provided in a lower portion at the left end of an area within which the carriage 101 is movable, enabling the ejection ports of the recording head to be capped while the apparatus is in a not-recording mode. That left end is called a home position of the recording head.
Reference numeral 107 denotes a switch portion and a display device portion. The switch portion is used, for example, when turning on/off a power supply of the recording apparatus and setting any of various recording modes. The display device portion indicates a state of the recording apparatus.
FIG. 16 is a perspective view of the recording head unit 103. In the illustrated unit, ink tanks 20A to 20C corresponding to respective color inks in black, cyan, magenta and yellow are replaceable independently of each other.
The carriage 101 mounts thereon a recording head 102 provided with a plurality of ejection ports for ejecting the inks in Bk, C, M and Y through them and a plurality of flow passages (nozzles) connected to the ink ejection ports, respectively, and four ink tanks, i.e., a Bk ink tank 20K, a C ink tank 20C, an M ink tank 20M and a Y ink tank 20Y. The ink tanks are connected to the recording head through connecting portions for supplying the inks to the nozzles from the tanks, respectively.
In addition to the above structure, there are also known recording head units in which, by way of example, tanks for inks in four color are integral with each other, or tanks for inks in C, M and Y are integral with each other, but independent of a tank for Bk ink.
FIG. 17 is a schema tic enlarged sectional view of a he at generating member and thereabout in the recording head. A heat generating member 30 comprising an electro-thermal transducer is arranged corresponding to an ink ejection port 23 in one-to-one relation. In a recording apparatus mounting thereon an,ink jet recording head thus constructed, an image is recorded by applying a drive signal to the heat gene rating member 30 of the head in accordance with recording information and ejecting ink from a nozzle. The heat generating member 30 can be drive n in an independent manner for each of all the nozzles. When the ink in the nozzle is quickly heated by energization of the heat generating member, a bubble is created in the ink due to film boiling and an ink droplet 35 is ejected toward a recording medium 31 under pressure developed upon the creation of the bubble, as shown in FIG. 17, thereby forming an image comprising characters or a picture on the recording medium. At this time, the volume of the ink droplet for each color ejected in such away is on the order of 15-100 ng.
The recording head has a plurality of ejection ports 23, a plurality of ink flow passages (nozzles) connected respectively to the ejection ports 23, and a common liquid chamber 32 formed rearward of a portion where the ink flow passages are disposed (i.e., on the upstream side) for supplying the ink to the ink flow passages. In each of the ink flow passages corresponding to the ejection ports in one-to-one relation, there are provided the heat generating member 30 for generating thermal energy used to eject an ink droplet from the ejection port, and an electrode wiring (not shown) for supplying electric power to the heat generating member 30. The heat generating member 30 and the electrode wiring are formed on a device board 33 made of, e.g., silicon by the semiconductor film deposition technique. A protective film 36 is formed on the heat generating member 30 to prevent the ink from coming into direct contact with the heat generating member 30. A partition wall 34 made of resin, glass or any other suitable material is placed on the device board to define the ejection ports, the ink flow passages, the common liquid chamber, etc. therebetween.
Such a recording system using the heat generating member is called a bubble jet recording system because a bubble created upon application of thermal energy is used to eject the ink droplet.
FIG. 18 is a typical block diagram for driving the recording head in the ink jet recording apparatus stated above.
Data of an image comprising characters or a picture to be recorded (referred to image data hereinafter) is input from a host computer to a reception buffer 401 in the recording apparatus 100. Also, data for confirming whether the data is transferred correctly or not and data for informing an operating condition of the recording apparatus are output from the recording apparatus to the host computer. The data in the reception buffer 401 is transferred to a memory unit 403 and temporarily stored in a RAM (Random Access Memory) under surveillance of a CPU (control unit) 402.
A mechanism controller 404 drives a mechanism portion 405, including a carriage motor, a line feed motor and so forth, in accordance with a command from the CPU 402. A sensor/SW controller 406 is a control unit for sending signals from a sensor/SW portion 407, including various sensors and SW""s (switches), to the CPU 402. A display device controller 408 is a control unit for controlling a display device portion 409, including LED""s, a liquid crystal display device and so forth on a display panel, in accordance with a command from the CPU 402. A recording head controller 410 controls a recording head 411 in accordance with a command from the CPU 402. The recording head controller 410 serves also as a control unit for sensing temperature and other information indicating a condition of the recording head 411 and transmitting the information to the CPU 402.
In such an ink jet recording apparatus utilizing thermal energy (called also a thermal ink jet printer), techniques for increasing a printing speed of the ink jet printer have been developed. The printing speed has been increased by, e.g., increasing the number of nozzles provided in one head or rasing the driving frequency.
An important point to be taken into consideration in the thermal ink jet printer is an excessive temperature rise of the recording head. In the thermal ink jet printer, the energy applied to the heat generating member in the head is not all consumed as energy required for ejection of the ink droplet and a large part of the applied energy remains as heat in the head. For that reason, when the thermal ink jet printer is constructed as mentioned above aiming an increase in printing speed, the amount of heat remaining in the head is further increased.
If a temperature rise of the head or ink is left as it is and not controlled in the thermal ink jet printer, this would not only make unstable an ejecting condition of the ink droplet, but also disable proper ejection of the ink droplet due to a resulting excessive temperature rise. In the worst case, there is a risk that the head may break down physically because of too much heat accumulated in it.
With the above problem in mind, several methods for preventing an excessive temperature rise of the head have been hitherto incorporated in driving/printing control of the thermal ink jet printer. There are proposed, for example, a method of detecting a head temperature and interrupting the recording for a predetermined time when the detected temperature is not lower than a predetermined value, and a method (Japanese Patent Publication No. 03-4394) of detecting a head temperature during the recording of one line, interrupting the recording after the end of the recording of that line when the detected temperature reaches a first prescribed value (i.e., when the head temperature rises excessively), and resuming the recording when the head temperature is lowered down below a second prescribed value.
There are also known methods for preventing an excessive temperature rise based on other parameters than the head temperature. One of those known methods is, for example, to make control based on both a detected result of the head temperature and a predicted result of the amount of temperature rise obtained by previously reading the recording duty of data to be recorded next (U.S. Pat. No. 4,910,528).
However, a rate of temperature rise or drop is not always constant because it greatly depends on the environment temperature around the head and the head temperature at that time. Accordingly, the above-stated method of interrupting the recording when the head temperature exceeds a threshold has had a problem that the interrupt time must be set to be longer than the least necessary time for ensuring safety and the recording speed may be eventually reduced as a whole. On the other hand, the method of previously reading the recording duty and predicting an amount of temperature rise has had a problem that if a prediction parameter is set in anticipation of the amount of temperature rise under high-temperature environment, this may result in overmuch control with a relatively large allowance under normal-temperature environment and also eventually reduce the printing speed in fact.
Further, when temperature control is performed in the above-mentioned thermal ink jet printer by using a result detected by a temperature sensor provided on the device board in the recording head, there is a difficulty in using an output value of the temperature sensor directly as the head temperature because individual temperature sensors have substantial errors in themselves due to variations in manufacture process. That problem can be overcome to some extent by suppressing variations in manufacture process of temperature sensors, but severer process control would, push up a head cost. In many cases, therefore, the output value of the temperature sensor is corrected and the corrected value is used in temperature control of the thermal ink jet printer. The correction of the sensor output value is however so complex that some error is mixed in the detected value even after the correction when conditions set for the correction are not optimum, and the purpose of control to be performed upon detection of an excessive temperature rise cannot be often fulfilled satisfactorily.
With the view of solving the problems as set forth above, an object of the present invention is to control a head temperature rise in a thermal ink jet printer during recording in a stabler manner, stabilize ink ejection, avoid failure of ink ejection, and to prevent thermal damage of an ink jet head.
To achieve the above object, the present invention provides a control method for an ink jet recording apparatus with which an amount of heat generated by an ink jet head is restricted when a condition of a head temperature being not lower than a predetermined threshold is found by the use of means for detecting the head temperature and an environment temperature around the head, wherein an extent of restricting the amount of heat generated by the head is changed depending on the environment temperature or a difference between the head temperature and the environment temperature. The present invention also provides an ink jet recording apparatus comprising means for detecting a temperature of an ink jet head, means for detecting an environment temperature around the head, means for restricting an amount of heat generated by the head when a condition of the head temperature being not lower than a predetermined threshold is found, and control means for changing an extent of restricting the amount of heat generated by the head depending on the environment temperature or a difference between the head temperature and the environment temperature.
With the above features, an excessive temperature rise of the ink jet head is prevented; hence failure of ink ejection and damage of the head can be avoided. In addition, since a standby time, extra split printing and so on which have been hitherto incorporated in the control process more than required are eliminated, the efficiency of recording is improved and higher-speed recording can be achieved as a whole.